The present invention relates to a method for measuring timber in accordance with the preamble of claim 1.
The invention also relates to an arrangement for measuring timber in accordance with the preamble of claim 9.
The present invention provides contact-free measurement of timber, whereby the method and arrangement can be applied not only to measuring timber during work, but also to making the measurement of timber in a wood handling machine more precise and to calibrating timber measuring devices known per se, for example.
In modern mechanical logging, especially in logging known as cut-tree or cut-to-length (CTL), ever greater requirements are set for the precision of measurement in the dimensions of the handled timber. In part, this is due to the fact that a great deal of timber trade is today based on measuring data collected automatically by a wood handling machine. A certain requirement for precision is then already established by legislation that relates to measurement in the timber trade. On the other hand, especially in logging based on the cut-to-length system, the benefits of precise measurement are emphasized when an entire tree trunk is considered in terms of after-felling optimization that provides the best possible use of the raw material.
Conventionally, mechanical logging requires at least the measurement of the diameter and length of the tree trunk or pieces cut from it. The measuring is done at a certain precision and allowed uncertainty of measurement.
During logging, the diameter of a piece of timber is measured generally by using mechanical tools that are set against the outer surface of the piece and that follow the outer surface during logging by measuring for instance the position of feeding and/or delimbing elements in relation to the body of the cutting head of the wood handling machine for the purpose of measuring the diameter. In measuring the length of the piece of timber, it is, in turn, common to use a hodometer that is pressed against the outer surface of the tree trunk and rolls along it as the tree trunk moves in the wood handling device. Thus, the hodometer measures the distance it travels on the outer surface of the tree trunk.
The methods described above are based on assumption and a measuring principle, in which an essentially round tree trunk is continuously in contact with the means used in measuring.
Common to all used measuring methods is that their precision needs to be regularly monitored. Measuring devices used in measuring the diameter and length of a piece of timber, for instance, need to be calibrated from time to time.
According to the prior art, a measuring device of a wood handling machine is calibrated for the diameter by means of specific calibration scissors and for the length by means of a conventional measuring tape, for instance, which requires a great deal of awkwardly performed manual work. It is worth mentioning, in particular, that, in practice, harvester work needs to be stopped completely for a time, when the operator has to come out of the control cabin of the forest machine to perform calibration measurements manually. When processing timber with a wood handling machine within its working area to cut them into desired lengths, the required calibration can be done in different ways. The operator of the wood handling machine then stops the machine after a chosen time and steps down to measure some of the sawn pieces. To do this, he also needs to know exactly the order, in which the pieces on the ground have been processed. Alternatively, the logging control and monitoring system of the forest machine is adapted to indicate the need to start a verifying measurement in connection with a random tree trunk.
Pieces of timber that are included in the calibration sample are measured in length, with a measuring tape, for instance, and diameter, with a large slide gauge, for instance, at as many points as deemed necessary. Today, the diameter is also generally measured using electronic calibration scissors made for this purpose as well as calibration gauges with means for automatically storing the measuring data and usually also a display for displaying the measuring data immediately to the person performing the calibration. Said electronic calibration scissors known per se can also operate interactively with the operator and indicate where the next calibration measurement should be taken.
In measuring the diameter of a tree trunk, errors are caused especially by a possible deviation in the shape of the cross-section from the ideal round shape, a varying and uneven surface pressure used in the measuring, and random errors caused by the person performing the measuring, for example. It is also possible that the person performing the calibration measurement mixes up two or more of the pieces of timber intended for calibration. The calibration may then provide a result that is notably false. This possibility of error is also furthered by the fact that calibration measurements are often performed in bad weather and lighting conditions. Pieces of timber may also roll to a different location on the ground than where the operator of the machine endeavours to place them. Problems in calibration measurement are also caused by the fact that pieces of timber often sink so deep in the snow or undergrowth that a proper cross-measure needed for the measuring cannot be measured. In addition, weather conditions, especially the melting and freezing of timber may affect the measuring result to some extend in calibration, too, not to mention the measuring performed by the harvester head.
In measuring the length of a tree trunk or pieces of timber, many other drawbacks also cause measuring errors. It should especially be kept in mind that the pieces of timber that are measured are more or less in the shape of a cut cone. This is a matter that unfortunately is often left unnoticed in the prior art. In other words, when calibrating a measuring device, the length of the outer or envelope surface of a piece of timber is often accidentally measured at some point of the surface of the piece. Thus, it is possible that the measuring tape is positioned parallel to the envelope of the cut cone of the tree trunk and the length value, thus, becomes greater than the length of the centre axis of the piece. The measuring of the calibration value for a desired length is done primarily visually and by free hand by keeping the measuring tape beside the piece of timber and trying to hold the measuring tape visually parallel to the centre axis of the piece.
The surface of a tree trunk often also has various problem and discontinuity points, such as stubs or a notably warped section, which may also cause errors in the measuring result. It is also possible and even probable that the ends of the piece of timber are not sawn fully perpendicular to the centre axis of the tree trunk. Especially a cut sawn on a butt log during felling or a cut in a warped piece of timber may differ quite a lot from an assumed ideal surface that is perpendicular to the centre axis of the piece.
In addition to the above-mentioned conventional measurements, requests have been made to be able to measure a few qualitative properties in terms of wood processing immediately during mechanical logging work. The determination and identification of knottiness, dry content, growth rate, growth ring structure and density, age, and especially factors diminishing quality, such as warp, rot, or some other defects, have been presented as additional information of interest.
In the prior art, monitoring and measuring qualitative properties of a piece of timber are done primarily visually, while it is the most important and, at the same time, most burdening work assignments for a user of a wood handling machine. A skilful user of a wood handling machine is able to estimate and monitor several different factors that affect the quality and value of the timber being processed in such a manner that it does not disturb efficient working. However, it is clear that as mechanical logging becomes more common and moves to new geographical areas, difficulties will be encountered in finding enough operators who are capable of quality determination and demanding, fast-paced decision-making. Therefore, there is a definite need for the automatization of the determination of quality properties in a piece of timber.